Traffic Engineering Studies Flashcards
What are the purposes of traffic engineering studies?
- to determine the characteristics of highway system users and their vehicles
- to monitor system operation
- to identify problem areas
- to assist in developing appropriate remedial action
Mean
average
Median
50th percentile value - half of values are more, half are less
Mode
the most frequent value of x
Standard deviation
measure of dispersion
Regression-to-the-mean
After a period of comparatively high crash frequency, it is statistically probable that the following period will have a comparatively low crash frequency
Delay
additional travel time experienced
Spot Speed
instantaneous speed of a vehicle passing a point on the roadway
Journey Speed
distance divided by the total journey time
Running Speed
distance divided by the running time
Time Mean Speed
arithmetic mean of spot speeds
Space Mean Speed
mean travel speed of vehicles traveling a roadway segment of a known distance
Capacity
maximum traffic flow that can be accommodated in a facility during a given time period under prevailing roadway, traffic, and control conditions
Purpose of travel time studies
Evaluate the quality of traffic movement along a route and determine the locations, types, and extent of traffic delays
Travel Time
elapsed time of travel
Running Time
time that the vehicle is actually in motion
Travel speed
overall average speed
Running speed
distance divided by running time
Fixed Delay
regardless of the amount of traffic
Operational Delay
interference from other components of the traffic stream
Control Delay
delay attributable to the intersection traffic control device
Purpose of No Passing Zone study
to establish limits on the roadway which permit the passing driver the necessary sight distance to allow a safe completion of the passing maneuver
Spot speed study
measures individual speeds of a sample of vehicles passing a point on the roadway
When should speed studies be conducted?
during off peak hours, when traffic is free flowing
What sample size is needed for spot speed studies?
100 vehicles per lane
Speed Zoning
establishment of safe, reasonable speed limits for certain sections of highway where the statutory speed limits do not fit the roadway and traffic conditions
A posted speed limit must be within ___ mph of the ___ percentile speed of free-flowing traffic
5 mph
85th
What factors may be considered when establishing speed limits?
1) Road characteristics, shoulder condition, grade, alignment, sight distance
2) Pace
3) Roadside development and environment
4) Parking practices and pedestrian activity
5) Reported crash experiencer at least a 12-month period
Pedestrian walking speed
3.5 feet per second
AADT
average annual daily traffic
average 24-hour volume at a given location over a full 365-day year
ADT
average daily traffic
average 24-hour volume recorded for some period less than a year
AWT
average weekday traffic
average daily traffic, M-F
DHV
design hourly volume
one-hour volume used as the basis of design or traffic operational decisions
Collision studies
Traffic safety studies that use crash reports to assess safety by evaluating number, type, and severity of crashes along a roadway segment or intersection
Gap study
determines the number of gaps in vehicle traffic that are of adequate length to permit pedestrians to cross the street
Site Impact Studies
determine the needs for any improvements to the adjacent and nearby transportation system to maintain a satisfactory level of service, safety, and access to a proposed land development
Site Impact Analysis steps
- site traffic generation
- site traffic distribution and assignment
- non-site traffic forecast
- analysis of LOS at intersections
- site access improvements
- internal site circulation and parking analysis
By federal law, every urbanized area over ________ population must have a transportation planning process
50,000
Areas with populations greater than __________ are designated transportation management areas (TMAs)
200,000
